CURRENT PROTOCOLS FOR ARTIFICIAL
INSEMINATION WITH CHILLED OR FROZEN
SEMEN
Tom A.E. Stout
Utrecht University, Department of Equine Sciences, Yalelaan 114, Utrecht,
The Netherlands
Introduction
The aim of an equine artificial insemination (AI) protocol is to ensure the
introduction of an adequate number of ‘fertile’ spermatozoa into the uterus of a
mare close enough to the time of ovulation to offer an optimal chance of
fertilization without otherwise compromising the ability to maintain pregnancy,
for example by provoking an intractable breeding-induced endometritis. The
exact protocol employed may, however, need to be adjusted to take account
of mare status and history, the exact stage of cycle at which the mare is
presented, prior knowledge of fertility and/or sperm longevity for the chosen
stallion, the availability of the semen (e.g. only on certain days of the week;
limited number of straws), whether payment is per straw, dose or pregnancy
and where the mare is to be managed (e.g. at a clinic, stud-farm or private
residence).
The major practical differences between chilled and frozen semen are the fact
that frozen semen is usually stored on site, whereas chilled semen needs to
be ordered 6 - 72 h before anticipated use, and the preferred timing of AI with
respect to ovulation. In this respect, it is generally assumed that chilled semen
will retain its fertilizing capacity for 24-48 h after insemination but that the
sperm require at least 4 h before they are ready to fertilize an oocyte, whereas
frozen-thawed spermatozoa are not expected to remain viable for much more
than 12 h but are thought to be capable of fertilizing much sooner after AI.
There is however considerable between-stallion variation in sperm longevity,
and indeed fertility; knowledge of minimum sperm number and maximum AIto-ovulation interval compatible with acceptable fertility for a specific stallion is
therefore extremely useful but, unfortunately, rarely available. The ultimate
aim is to ensure the presence of live capacitated spermatozoa in the caudal
ampulla of the oviduct shortly after the arrival of the oocyte, and certainly
before the oocyte begins to degenerate. This presentation will discuss the
strategies for achieving this aim, and the factors that may dictate or influence
the management of AI.
Is one insemination enough?
It has long been maintained that a single AI per cycle should be the preferred
strategy because it will minimize the risk of provoking a persistent breedinginduced endometritis and thereby maximize the chance of pregnancy. There
are also other valid reasons for preferring to minimize the number of
inseminations per oestrus, for example because a stallion is very popular or
because very few straws of frozen semen are available and/or the semen is
15-‐18
February
2016
East
London
Convention
Centre,
East
London,
South
Africa
114